Re: [PATCH v3 4/6] ext4: reorder map.m_flags checks in ext4_iomap_begin()

Jan Kara
2019-09-23T15:08:45Z

On Thu 12-09-19 21:04:30, Matthew Bobrowski wrote:
> For iomap direct IO write code path changes, we need to accommodate
> for the case where the block mapping flags passed to ext4_map_blocks()
> will result in m_flags having both EXT4_MAP_MAPPED and
> EXT4_MAP_UNWRITTEN bits set. In order for the allocated unwritten
> extents to be converted properly in the end_io handler, iomap->type
> must be set to IOMAP_UNWRITTEN, so we need to reshuffle the
> conditional statement in order to achieve this.
>
> This change is a no-op for DAX code path as the block mapping flag
> passed to ext4_map_blocks() when IS_DAX(inode) never results in
> EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN being set at once.
>
> Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
> Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> fs/ext4/inode.c | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 761ce6286b05..efb184928e51 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3581,10 +3581,21 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> iomap->type = delalloc ? IOMAP_DELALLOC : IOMAP_HOLE;
> iomap->addr = IOMAP_NULL_ADDR;
> } else {
> - if (map.m_flags & EXT4_MAP_MAPPED) {
> - iomap->type = IOMAP_MAPPED;
> - } else if (map.m_flags & EXT4_MAP_UNWRITTEN) {
> + /*
> + * Flags passed to ext4_map_blocks() for direct IO
> + * writes can result in m_flags having both
> + * EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN bits set. In
> + * order for allocated unwritten extents to be
> + * converted to written extents in the end_io handler
> + * correctly, we need to ensure that the iomap->type
> + * is also set appropriately in that case. Thus, we
> + * need to check whether EXT4_MAP_UNWRITTEN is set
> + * first.
> + */
> + if (map.m_flags & EXT4_MAP_UNWRITTEN) {
> iomap->type = IOMAP_UNWRITTEN;
> + } else if (map.m_flags & EXT4_MAP_MAPPED) {
> + iomap->type = IOMAP_MAPPED;
> } else {
> WARN_ON_ONCE(1);
> return -EIO;
> --
> 2.20.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR